Assessing the safety of new germicidal far-UVC technologies.

The COVID-19 pandemic underscored the crucial importance of enhanced indoor air quality control measures to mitigate the spread of respiratory pathogens. Far-UVC is a type of germicidal ultraviolet technology, with wavelengths between 200 and 235 nm, that has emerged as a highly promising approach for indoor air disinfection. Due to its enhanced safety compared to conventional 254 nm upper-room germicidal systems, far-UVC allows for whole-room direct exposure of occupied spaces, potentially offering greater efficacy, since the total room air is constantly treated. While current evidence supports using far-UVC systems within existing guidelines, understanding the upper safety limit is critical to maximizing its effectiveness, particularly for the acute phase of a pandemic or epidemic when greater protection may be needed. This review article summarizes the substantial present knowledge on far-UVC safety regarding skin and eye exposure and highlights research priorities to discern the maximum exposure levels that avoid adverse effects. We advocate for comprehensive safety studies that explore potential mechanisms of harm, generate action spectra for crucial biological effects and conduct high-dose, long-term exposure trials. Such rigorous scientific investigation will be key to determining safe and effective levels for far-UVC deployment in indoor environments, contributing significantly to future pandemic preparedness and response.

Origins and Evolution of Photocarcinogenesis Action Spectra, Including Germicidal UVC†.

Germicidal ultraviolet radiation (GUV) provides a means of dramatically reducing airborne spread of microorganisms in residential and workspace environments. Regarding design and use of GUV, both efficacy and safety data have accumulated over several decades, with a substantial increase of attention during the current COVID-19 pandemic. Considerations for skin and eye safety previously resulted in guidance on exposures in institutional and workplace settings. This report details the evolution of limits for skin exposures, with particular attention to the risk of skin neoplasia.

The effect of 222-nm UVC phototesting on healthy volunteer skin: a pilot study.

BACKGROUND: Frequent topical antiseptic use to hands is now common in healthcare and other work environments. Inevitably, the use of such antiseptics will present an occupational risk for irritancy and allergic dermatitis. New, less irritant and even non-chemical antimicrobial approaches are under investigation. METHODS: A Sterilray disinfectant source (222 nm) conventionally used to sterilize equipment and work surfaces was assessed for tolerability in human skin. Using an escalating dosage study methodology, four skin phototype I and II healthy volunteers had their minimal erythema dose (MED) determined. Punch biopsies of irradiated sites were stained for cyclobutane pyrimidine dimers (CPD). The degree of CPD was compared with that in biopsies from unexposed skin and from areas exposed to UVB (280-315 nm) radiation. RESULTS: Calibrated spectral measurements revealed emission at a peak wavelength of 222 nm with 97% emission at wavelengths less than 250 nm. At low doses below the threshold bacteriostatic effect, the source was capable of inducing both erythema and CPD formation in human skin. In two individuals, cells in the basal layer were not shielded by the overlying tissue as indicated by the presence of CPD. CONCLUSION: The source showed an erythemogenic or CPD potential at lower doses than those required to reach the reported threshold bacteriostatic effect.

Miniature swine model of phototoxicity testing.

BACKGROUND/PURPOSE: This study determined the threshold doses for 'solar erythema' and for phototoxic responses to 8-methoxypsoralen (8-MOP) in white skin Hanford and grey skin Yucatan miniature swine. METHODS: For threshold erythema determinations, the UVR exposures included both UVA (315-400 nm) and UVB (290-315 nm) radiation by positioning one fluorescent 'sunlamp' among 10 'PUVA' lamps. With this configuration the UVR exposures ranged from 0.5-2.8 times the 'instrumental MED' (MEDi) for Hanford and from 1.0-5.6 times the MEDi for Yucatan. For phototoxicity determinations (i.e., with and without topically-applied graduated concentrations of 8-MOP), the UVB component was minimized by extinguishing the sunlamp, thus permitting higher UVA exposures. RESULTS: The Hanford had the lower UV erythema dose threshold (1.0-1.4 times the MEDi) and the erythema that developed was readily observable. The exposure doses for the phototoxicity test were 5 J/cm(2) of UVA in 35 minutes or 10 J/cm(2) in 70 minutes. The phototoxic (vascular) response to 8-MOP was observed in the two highest concentrations (0.01% and 0.1%) in Hanford pigs, in a dose-related manner. Microscopic evidence of a dose-related response was also observed as the concentration of 8-MOP increased. CONCLUSION: This verified that the Hanford miniature swine is the preferable strain for phototoxic effects. In contrast, UVR exposure of the Yucatan pig skin produced tanning rather than erythema, confirming that the Yucatan is the more appropriate strain for studying the melanization response. Thus, Hanford and Yucatan miniature swine have cutaneous photobiological responses that reflect their respective strain differences.

Moisturizers, vehicle effects, and photocarcinogenesis.

Topically applied formulations (e.g., emollients and moisturizers) may influence the optical physics of skin and therefore the effectiveness of UVR exposures. In this issue, Lu et al. provide evidence for another type of influence by moisturizers, one that does not require the presence of the chemical agent before or during UVR exposure. Several such test agents applied after the completion of a course of UVR enhanced the tumor response in mice, both qualitatively and quantitatively. The study design is rational but the group sizes are modest, the resulting database is therefore limited, and the repeatability is not yet determined. Perhaps most important for the this Journal's readership, the clinical relevance is unknown and deserves detailed examination.

Ultraviolet tanning equipment: six questions.

Recreational tanning, particularly as promoted by commercial salons with 'sunbeds' or booths, has generated increasing attention from the regulatory and the biomedical communities. Several agencies have weighed in with opinions on recommended modifications in guidelines, training procedures, regulatory controls, and consumer awareness. Currently there is little uniformity in the guidance provided by trade groups, in recommendations supplied by health agencies and medical associations, or in regulatory approaches taken or proposed by the many countries involved. In an effort to provide a clearer focus for its concerns in this area, the EU Directorate General Health and Consumer Affairs formulated six questions on ultraviolet (UV) tanning, all of a technical or biomedical nature. The questions were stimulated in part by the fact that the European Commission no longer regards the European standard EN 60335-2-27:1997 ('Particular requirements for appliances for skin exposure to ultraviolet and infrared radiation') as giving presumption of conformity to the Low Voltage Directive 73/23/EEC. (The latter Directive governs marketing of electrical devices in EC countries.) Initially, the questions were posed to an EU Scientific Committee. Subsequently, industry representatives and the European Commission jointly requested that the scientific community provide answers to the questions. We received the questions with a request for our technical responses and opinions. Our response was in the form of the following essay, submitted earlier this year to the European Commission. We offer it here in the hope of stimulating constructive discussion and comment.